Differential volume control for diversity reception



H. H. BEVERAGE DIFFERENTIA-L VOLUME CONTROL FOR DIVERSITY RECEPTION Filed Dec.

Nov. 15, 1932.

Patented Nov. 15, 1932 UNITED STATES PATENT oFFlcEfi" v HAROLD n. BEVERAGE, oF EIVEEHEAD, NEW Yonx, AssIGNoR To RADIO .cor'uoRA'rIoiv oF AMERICA, A CORPORATION or DELAWARE DIFFERENTIAL VOLUME CONTROL FOR DIVERSITY RECEPTION Application meaDecembeVr-n, 192s. serial No. 325,304.

This invention relates to diversity reception, and more particularly toa method. and means for advantageously regulating the output from a plurality of antennas. Short wave signals are subject to fading which varies both in frequency and degree in an unpredictable manner. Inasmuc'h as the fading `at any instant may differ very Widely at geographically spaced points, or in different planes of polarization, it has been suggested that a receiving station be equipped With a number of antennas having different fading characteristics,the energies Lcollected by which are fed to a single signal responsive means.

Experience has shown that high frequency 4energy fluctuates not onlyl in intensity but Valso in phase, and that theremay be considerable relative phase fluctuation at the several antennas. impossible to directly combine the radio vfrequency energies, `for the energies may as often be in phase opposition as in like phase, to overcome this difficulty kit has been suggested to equip each of the antennas with a separate receiver, and to combine the energies after rectification, andrthis, in the case of code signals, has proven an apt solution.

However, I have found that in the case'of speech telephony, or other speech-simulating signals, Where thetransmission energy is radiated in the form of a carrier and side bands, there may be a relativevdifference in the phase fluctuations of closely adjacent frequencies, such` as side band and carrier frequencies, even at one antenna, just as there is between carriers of like frequency at different antennas. This causes similar phase fluctuations in the beat of the carrier and side bands, for if of two beating Waves Aone is kept constant in phase,Y While the other is shifted in phase, their beat is equally shifted in phase. It consequently follows that although the carrier and side bandenergies experience only radio frequencydifferences in phase, these differences are trans-V ferred to` the detected or audio frequency energies, so that 'it is as impossible to combine the detected energies as it is to directly This phenomenon makes vit v ergies.

combine the roriginally collected radio frequency energies.

lVith 'the usual type of*` diversity system, even if applied merely to code signals, the received energy is apt to vary between the extremes -of` almost complete fading atv all ofthe antennas to no fading at any of the antennas. To overcome this it has been suggested to employ a volume controlwithiea'ch kantenna for varying the gain in the amplifier,... coupled thereto.` Such an arrangement suffers from the disadvantage that the increased .gain givenan amplifier of .an antenna at which fading Vis prevalentincreases the noise level in the output of that amplifier, ,and 65 therefore in the combined outputfof the en- 4tire system. Furthermore, in the case of speech-simulating signals, in the event of Y fading ofthecarrierand notof the side bands at an antenna its yamplifier is given increased gain,'as a result of. which the 'beat between the sidebands is unduly amplified before being combined with the output from the other antennas, thereby creating augmented :distortion. f

In order to overcome the-foregoing difficulties I propose to select from among the several antennas that-antenna at which the 're-y for energizing the final signal responsive Y means. In this wai/'there is little conflict due 'to relative-phase fluctuations at the different i antennas, and a considerable amount of volume control is provided merely in using subvstantially only one antenna at a time. Furthermore, an antenna at AWhich the carrier alone has faded is vgiven diminished output, and therefore has but little eect onthe receiver, which reduces distortion. Y

In order to effectl smooth operation, and to. simplify the necessary apparatus, I donot physi-cally disconnect all of the antennas but one, but rather permit them to remain in circuit, and regulate their outputs by controlling the amplification of` their respective 4en- In terms of a method, my invention includes simultaneously making'la plurality Vof separate energy collections of relatively 100 different fading characteristics, preferably by collecting the energy on a plurality of geographically spaced antennas, separately amplifying each of the collected energies, controlling the gain in the aforesaid step of amplification of the energies in accordance with the amplitudes of the other energies, in order to strengthen the maximum signal or greatly magnify the ratio of the initial signal strengths, even to the point of completely cutting 0E a weaker signal, thereafter combining the energies, and translating the combined energy.

The foregoing method is unstable, because with even a very slight initial difference in the signal strength, the stronger signal is amplified, which then weakens the weaker signal, which then serves to more greatly. amplify the'stronger signal, so that almost instantaneously the weaker signal is completely cut out, while the stronger signal is greatly amplified. Thereafter the arrangement will not function to receive energy from the antenna. which has been cut out, even though its signal shouldgrow stronger, except if the signal on the antenna which before was a "maximum should fade practically to zero, in which event the'amplification gain is shifted rapidly, so as to greatly amplify the signal which then is a maximum. While this ar -rc n gement has the advantage of selecting the best'antenna in a verypositive manner, much flike a mechanical relay, it has the great disadvantage of making the transition from one antenna to another distinctly audible, with a somewhat disturbing sudden change in volume. Y

To overcome this difficulty and make the change-over from one signal to another more stable and less noticeable, is a further ob- .ject of my invention, `which I accomplish by .controlling the gain in the amplifiers only partially in accordance with the magnitude vof the other energies, and partially in accordance with the magnitude of the energy being controlled. For this purpose I use a plurality of amplifiers with each antenna, and VI couple the volume. control means folllowing the last amplifiers with amplifiers of vcorresponding antennas as well as with amrplifiers of the other antennas. To more con- .cretely fix the ideas involved, suppose two antennas are used. I then employ a first and and a second electron emission tube amplifier for eachof the two antennas, and I couple the volume control means following each of `the second amplifiers with the first amplifiers of the corresponding antennas and the second amplifiers of the other antennas. In this manner the energy supplied to the translating device is kept constant by reason of the normal volume control operation of the first amplifier. However, if the signal should weaken so much that the first amplifier, when given maximum gain, still cannot keep the signal up to the desired level, the second amplifier of the other antenna begins to be made conductive, and energy passing therethrough makes the second amplifier of the formerly active antenna grow non-conductive, and at the same time makes the first amplifier` of the now active antenna attain such a. bias as will supply the desired constant amount of energy to the translating device. The antenna which is cut out'by reasonlof its second amplifier being negatively biased, at the same time has its first amplifier made highly conductive, which permits admission of the cut out signal init-s turn with little or no initial difference in signal amplitude. A Y

- To attain substantial independence of the relative radio frequency phase at the different antennas it is desirable to combine lthe energies after rectification. At the same time,

the volume control means preferably com` prise detector tubes with impedan'ces in their anode circuits from which th-e amplifier bias potentials are obtained through electrically slow circuits. For simplicity I combine the rectified energies obtained from the volume control detectors, thus dispensing'with separate detectors, and this combination may vbest be made through coupling tubes connected to the detectors. the output of the coupling tubes being fed to a common translating device. f 1

My invention is described more fullylin the following specific'ation`,which is accompanied by a drawing in which Figure l is a wiring diagram for a form of my invention employing two antennas; Y

Figure 2 is a modification showing how my invention may be applied toa system having more than two antennas;

.Figure 3 indicates an alternative form of bias lead connection when two antennas are l employed; and

Figure 4 indicates an alternative form of biaslead connection when three antennas are employed. L

*Referring vto Figure l of the drawing, there are aplurality of antennas 2 and. Il, which are arranged to have different fading characteristics, either by being positioned inY different planes of polarization or` more prefl erably, by being geographically spaced a substantial distance apart relative to the working wave length, or both. The antenna 2 is coupled by a transmission line 6 to a first amplifier 8. which in turn leads to a second amplier 10. while the antenna 4l is coupled by a transmission line 12 to a first amplifier '14, which leads to a second amplifier lf3. The amplified outputs are fed to detector tubes 18 and 20, which also act as volume con` trol detectors. The anode circuits of the tubes include low pass filters 22 and 24e.' and sources of direct anode potential 26 and 28,

and connected in series therewith, the conpling impedances 30and 32, which complete' feo f the :anode circuits to ground. Arranged in parallel with the coupling impedances `are electrically slow circuits comprising the resistances 34 and 36, in series with. the lcon- `densers 38 and 40, the relative magnitudes of which determine the time constant of the volume control action.

From the volume control circuit 34, 38 a lead 42, 44 is led to the control electrodes of the tubes in the amplier 16` while from the volume :control circuit 36, 40 a lea-d 46, 48 is run tothe control electrodes of the tubes in the amplifier 10. In this manner the amplifiers are made more orless conductive in accordance with Whether the energies flowing through are greater or smaller, respectively, instead of vice versa as is ordinarily the case, so that the stronger signal is strengthened,

the weaker signal is weakened and due to the.

cumulativeness of this action the amplifier of the weaker signal is soon sufciently negative 'so that that signa-l is cut out.

This actionis sulliciently abrupt and unstable to be noticeable to the ear, and to avoid this, I connect the volume control circuit 34, 38 by means of a lead 50 to the amplifier 8 vand the volume control circuit 36, 40 by a lead 52 to the amplifier 14. This volume control functions in ordinary fashion, and serves tokeep the volume of the signal being utilized at a desirable level, land at the same time, makes the change-over from one antenna to another practically unnoticeable because the nal energy output to which the translating device is responsive is always `keptat the desired signal level.

In order .to couple the two receivers to a singletranslating means, which I shall term combining the energies even though one may be zero much .of the time, the coupling Yimpedances 30 'and 32 are each led to coupling tubes 54 and 56 through blocking conldensers `58`and 60. The controlelectrodes of the tubes are biased by batteries 62 and 64,

and the-anode circuits are connectedtogether,

Y as shown, and, through a transformer66, to

a common translating device here exemplified by a loud speaker 68. The anode circuit is then completed to a source of direct Aanode potential and to ground.

My invention may be applied 'to systems `having any number of antennas, it being control circuits 162, 164, and 166. The desired signal is fed to coupling tubes v'172, 17 4, l

,also may beexpa'nded to accommodate .and17 6, the outputs of'whichware combined together and fed to .a translating vdevice 68. It will be observed that this arrangement is substantially like that shown in Figure 1 except for the addition of another set of amplifiers. f v. Y

Inspection of the wiring diagram` will show that each of the electrically/slow volume control circuits are coupled to the control electrodes of the tubes in the correspondingr firstzamplifier, andalso to t-hecontrolV electrodes .of the .tubes in either the secondV or the third amplier of the other antennas.

"Thus, with the maximum signal received yon antenna 102, the volume control circuit 162 jwillbias the amplifiers 144, 'and-',136 to cutv ofi", While a maximum signal on the'antenna -104V will Vcause the volume control circuit 164V tobias the amplifiers 142 and 146 to cut off,

and a maximum signal on the antennaz106'` willcause thevolume control circuit 166 to bias the ampliers 132 and 134 to cut ofi", so that at ally timesone of the signals will be amplified substantially to the exclusion of the otherV signals. Meanwhile the connections from` the volume control circuits through which weaker signals are passing to the second and third amplifiers of the antenna collecting the maximum signal serve -to boost, the-amplification gain of the maximum signal, resulting inV a cumulative ,-difference, as in the arrangement in Figure 1. However, instability is overcome by the bias leads running directly from each of the-:VOL ume control circuits to the corresponding first amplifiers. .A

It is notV essential that the bias lead connections be made exactly-,as in Figures 1 and 2. For example, the connections may be arranged as in Figures 3 :and 4, in which all of the first amplifiersare `coupled together and -to-a volume control unit, whileall of the .second amplifiersare vcoupled together and to a second volume control unit, and, in the case of Figure 4, all of the third amplifiers are coupled together and to a third volume control unit. Obviously, this arrangement any desirednumberof antennas. f Y y However, I consider that the arrangement ,iodo

shown in Figures 1 and 2, in whichthe true volume controlaction is applied to corresponding amplifiers, Ymore specifically, to the firstV amplifiers, is slightly preferablyr bel cause it permits of the use of a different number of stages of amplification in the first amplifiers, relativeto the further amplifiers, should that prove desirable in order toV attain smooth operation. Of course, the same result may be accomplished inthe arrangementsv shown in Figures 3V and 4,by using the desired number of stages of amplification in that amplier which is employed for direct volume control action, thus, in Figure 4, the

first amplifier of the first antenna, the sec- 30nd amplifierof the second' antenna, and the Vthird amplifier ofthe third antenna. However, this upsets the symmetry of the receivers, and furthermore, is complicated by the fact that the gain in an amplifier' may differ, when receiving a large input, from the gain when receiving a very small input.

I claim: l

l. The method of diversity reception which includes making a plurality of energy collections having different fading characteristics, separately amplifying each of the collected energies, controlling the gain in the aforesaid step of amplification ofthe energiespartially in accordance with the magnitude of the other energies, and partially in accordanceV with the magnitudeof the energy in question, in order to strengthen the maximum signal and to make the change overV ther amplification in accordance with the output of the other energies, combining the final output energies, and translating the combined energy.

3. The method ofdiversit-y reception whichv includes making a plurality of energy collections at geographically spaced points,

'separately amplifying each of the collected energies, separately further amplifying each Vof theA amplified energies, controlling the gain in' the'first step of amplification in accordance with the corresponding Vfinal output, controlling the gain in the further amplification in accordance with the output of the other ener ies combinin the ener ies and translating the combined energy.

4. The method of diversity reception which includes making aplurality'of energy collections of different fading characteristics, separately amplifying each of the-collected energies a plurality of times, rectifying the amplified energies, controlling the gain 'in some of the steps of amplification in accordance with t-he amplitude of the corresponding rectified energy, controlling the gain in the other steps of amplification in accordance with the amplitude of the other rectified energies, combining the rectified energies, and translating the combined energy.

r5. The method of Y diversity reception which includes making a plurality of energy collections at geographically spaced points,

separately amplifyingeach of the collected energies, separately further amplifying sponding rectified energy, controlling the gain in the further amplication in accordance with the amplitude of the other rectified energies, combining the rectified energies, and translating the combined energy.

6. A diversity receiving system comprising a plurality of antennas having different fading characteristics, an amplier coupled Ito each of the antennas, volume control means following each of the amplifiers, and means so coupling each of the volume control means to the amplifiers as to control the gain in the amplifiers partially inV accordance with .the magnitude of the energies from the other amplifiers, and partially in accordance with theV magnitude of their own outputs, in order'to strengthen the maximum signal and to make the change-overl from one signal to another more stable and less noticeable, means to combine the volume controlled energies, and means to translate the combined energy.

7. A diversity receiving system comprising a plurality of geographically spaced'antennas, an amplifier coupled to each of the antennas, further amplifiers coupled to each of the first amplifiers, a rectifier coupled-to each of the 'last amplifiers, a volume control impedance in each of the rectifier circuits, means coupling the volume control impedances to corresponding first amplifiers and tov the further amplifiers of the other antennas, means to combine the rectified energies, and means to translate'the combined energy.

8. A diversity receiving system comprising two geographically spaced antennas, an electron emission tube amplifier coupled to each ofthe antennas, a second electron emission tube amplifier coupled to each of the first amplifiers, a detector coupled to each of the second amplifiers, a volume controlling bias lead connected from the anode circuit of l each of the detectors-to thecontrol electrodes of the tubes inthe corresponding first amplifier and to the control electrodes of the tubes in the other second amplifier, means to combine the rectified energies, and means to lating device, and means coupling the anode circuits of the coupling tubes togetherV and to the translating device.

10. A diversity receiving system comprising three geographically spaced antennas, an electron emission tube amplifier coupled to each of the antennas, second and -third electron emission tube amplifiers coupled to each of the first amplifiers, a detector coupled to each of the third amplifiers, a volume control lo bias lead connected from the anode circuit of each of the detectors to the control electrodes of the tubes in the corresponding rst amplifiers and to the control electrodes of the tubes in one of the second and third ampli- ,5 fiers of the other antennas, a coupling tube connected to each of the detectors, a translating device, and means coupling the anode circuits of the coupling tubes together and to the translating device. 2u HAROLD H. BEVERAGE. 

